The present invention relates generally to determining the dynamic state of an automotive vehicle, and more particularly, to a method and apparatus for determining lateral velocity of an automotive vehicle.
Stability control systems are increasingly being used on automotive vehicles to improve the stability of the vehicle during operation. Such systems use the vehicle lateral velocity in determining the dynamic state of the vehicle. Lateral velocity may be directly measured by instrumental sensors such as optical sensors or global positioning sensors. However, there are practical considerations such as high cost, signal degradation, and lost of signal during certain weather/environment conditions that inhibit production vehicles from using these sensors presently.
Various types of lateral velocity estimation techniques have been proposed. Each, however, has undesirable drawbacks which may lead to inaccurate lateral velocity determinations. For example, one known method assumes that the tires are operating in a linear. region with known cornering stiffness. However, as in many circumstances, the tires may not operate in a linear region during the changing dynamic states of the vehicle.
Another important factor in determining lateral velocity of a vehicle is measurement noise and the effect of measurement noise on the lateral velocity determination. To provide a robust system, the measurement noises from such sensors as lateral acceleration or velocity must be minized and must not excite errors in convergence algorithms. One significant source of measurement noise to consider is the variation in road bank and/or vehicle attitude.
In the paper by Kaminaga and Naito, xe2x80x9cVehicle Body Slip Angle Estimation Using An Adaptive Observerxe2x80x9d, an adaptive observer using a sliding mode approach is proposed. However, this approach requires the estimation error of lateral velocity as an input to the parameter adaptation algorithm to guarantee stability. This, of course, is not possible since the true lateral velocity is not known. Then, the estimation error in the lateral velocity derivative is used as a substitute signal. It is argued that the effect of cornering stiffness (i.e., the adapted parameter) will have a similar effect on both the error of lateral velocity and the error of its derivative. Although the argument may be valid for certain low frequency maneuvers, it is believed to be inaccurate for other maneuvers. Without the robustness property for a wide variety of maneuvers that a vehicle may experience, their approach is undesirable for use in a dynamic control system of a production vehicle. Furthermore, such a system also is believed not to compensate for sensor bias experienced during a banked road condition.
U.S. Pat. No. 5,676,433 also proposes a device for estimating side slide velocity of a vehicle. The side slide velocity is determined by integrating on a time basis the difference between a lateral acceleration detected by the lateral acceleration detection: means and the product of the yaw rate and the longitudinal velocity by using only the high frequency components of the lateral acceleration and yaw rate. This approach, of course, is very sensitive to the inaccuracy of all the above signals since the integration procedure substantially amplifies low frequency error. Since the ""433 patent suggested a high pass filtering process, the method cannot differentiate a sustained increase/decrease in lateral velocity (i.e. real signal in low frequency/dc) from a sustained low frequency/DC sensor noise.
It is therefore one object of the invention to provide a robust determination for lateral velocity of the vehicle that maintains high accuracy by incorporating or compensating for various dynamic conditions of the vehicle.
It is therefore one object of the invention to provide an improved method and apparatus for determining lateral velocity.
In one aspect of the invention a method for determining lateral velocity of a vehicle comprises the steps of:
determining an -unbiased lateral velocity derivative;
creating a fictitious lateral velocity estimation error; and,
determining a lateral velocity by feeding the fictitious lateral velocity estimation error into an adaptive observer.
One advantage of the invention is that various dynamic conditions of the vehicle are taken into consideration such as, transitioning road surfaces, varying corner stiffness, road surfaces and bank angle variations, and various sensor constraints.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction -with the attached drawings and appended claims.